Recirculating thermosyphonic heat exchangers



p 8, 1970 R. RUTHERFORD 3,527,292

RECIRCULATING THERMQSYPHONIC HEAT EXCHANGERS Filed Dec. 15, 1967 RONALD RUT HERFDRD mvannl' United States Patent 3,527,292 RECIRCULATING THERMOSYPHONIC HEAT EXCHANGERS Ronald Rutherford, Sunder-land, England, assignor to Washington Engineering Limited, Washington, Durham County, England Filed Dec. 15, 1967, Ser. No. 690,968 Int. Cl. F28d 15/00; F28f 13/08; H01f 27/10 US. Cl. 165106 5 Claims ABSTRACT OF THE DISCLOSURE A heat exchanger comprising a top and bottom header and a plurality of spaced fiat sections extending side by side between the headers. The internal cross section of each section varies along its length and is greatest at that end connected with the top header. Preferably the spacing between the side walls of each section is constant and the width of the section increases progressively along its length. The 01 each side of a section may be formed at spaced points with depressions of elongated shape, inclined to the longitudinal axis of the section, such that the side walls contact to form obstructions which cause liquid flowing through the section to follow a more or less tortuous path.

This invention relates to heat exchangers and particularly to heat exchangers of the kind which are used for cooling electric transformers operating under so- -called ON conditions where the transformer has no moving parts and is cooled by heat transfer between oilsteel and air, and under OB conditions which are essentially the same except that the natural flow of air over the heat exchanger is supplemented by the action of fans. Such heat exchangers normally consist of a plurality of tubes or sections extending between the top and bottom headers and in the case Where sections are used these ordinarily comprise two half-sections of sheet material which, after forming, are joined together at their peripheral flanges. In use, the top and bottom headers of such heat exchangers are connected respectively with the upper and lower parts of the transformer tank and the oil therein circulates through the heat exchanger by thermo-syphon action, hot oil at the top of the tank entering the heat exchanger and on cooling therein flowing downwards to the bottom header and then back to the lower part of the tank.

As hitherto constructed, the tubes or sections of such heat exchangers are of constant cross section along their length between the headers. It has now been found that better efficiency is achieved if, in accordance with this invention, the cross section of the sections is varied along their length such that it is greater at that end adjacent the top header. Such an arrangement alfords a greater surface area from which to dissipate heat in that part of the heat exchanger which contains the hottest oil and an improved performance is thus obtained as compared with the case where the cross section is uniform. Moreover the change in cross section tends to disturb a lamina flow of the liquid which again tends to improve performance.

A further improvement in performance may be obtained if in accordance with a feature of the invention the sections are formed so as to produce periodic changes in direction of flow of the liquid therethrough. Such effect may be obtained by forming one or each halfsection with depressions such that when the sections are assembled they contact at one or more places to form an obstruction which is inclined to the longitudinal axis and is disposed between the longitudinal side edges,

3,527,292 Patented Sept. 8, 1970 whereby the liquid flowing through the section is caused to follow a more or less tortuous path.

A further improvement in performance may be obtained if in accordance with a further feature of this invention the sections are connected with the two headers, not symmetrically as is customary, but at their outer corners whereby to leave a clear unobstructed path for the flow of air over the section.

The invention is illustrated by way of example in the accompanying drawings, in which:

FIGS. 1 and 2 are a side elevation and an end elevation of one form of heat exchange and FIG. 2 shows it associated fragmentarily with an electric transformer tank;

FIG. 3 shows a detail of FIG. 2 to a larger scale, and

FIG. 4 is a section on the line A-A of FIG. 3.

Referring to the drawings, the heat exchanger there shown comprises a plurality of sections 1 connected between top and bottom headers 2, 3, the sections being constructed in conventional manner by welding together two formed half-sections along their peripheral flanges 4.

From FIG. 2 it may be seen that the sections are of tapered shape, being wider at their upper ends, with the result that, the spacing of the two sides being constant, the internal cross-section varies progressively along the length instead of being constant as in conventional constructions.

From FIG. 2 it may also be seen that each section 1 is connected with the headers 2, 3 at its corners instead of centrally between its longitudinal side edges as is conventional.

In the illustrated embodiment the two headers, 2 and 3, are each of triangular section and may be formed from sheet material which before forming may be suitably slotted to receive the corners of the sections to which they may be joined in a fluid-tight manner by welding. Also shown in FIG. 2 is a fragmentary portion of a conventional electric transformer tank T with which the heat exchanger is connected via suitable pipe connections 2a and 3a.

As shown in FIGS. 2, 3 and 4, the sections are specially formed so as to produce periodic changes in the direction of flow of liquid therethrough. As shown, each half section is provided during the forming operation with a plurality of depressions 6 which in plan are roughly of triangular shape and which are of such maximum depth that when half-sections are assembled and the depressions are in contact over a limited area 7 and may be welded together at these points.

As may be seen from FIG. 2, these depressions are so positioned that they incline alternately in opposite directions from the central longitudinal axis of the section and accordingly the liquid flow through the section tends to be deflected first towards one edge of the section and then towards the other edge.

The improved heat exchanger of this invention is particularly suitable for use in cooling transformer oil when circulation is effected by thermo-syphon action but is not so effective when forced circulation is used since owing to the increased velocity of flow there will only be a small temperature differential between the top and bottom headers.

I claim:

1. An improved heat exchanger of the thermo-syphonic type for generally Vertical disposition, in combination with an electric transformer casing wherein cooling oil circulation is effected by thermo-syphonic action with the oil being fed into the top and out of the bottom without use of forced circulation means, said heat exchanger comprising vertically spaced apart top and bottom headers; a plurality of spaced, relatively flat tubular cooling sections extending in vertical, flat side-by-side relation between and interconnecting with said headers; each of said sections embodies opposed side walls and the lateral spacing between the side walls is substantially constant; and wherein the internal cross-section width of said flat cooling sections varies progressively along the sections vertical length and is greatest at that end connected with said top header.

2. A heat exchanger as claimed in claim 1, wherein the sections are each connected with the top and bottom headers adjacent the respective ends of one longitudinal edge of the section.

3. A heat exchanger comprising:

(a) a top header and a vertically spaced bottom head- (b) a plurality of flat, cooling sections extending in spaced, side-by-side relation between and interconnecting said top and bottom headers;

(c) said sections each having substantially constantly spaced sidewalls, and an internal fore-and-aft directed cross-sectional width which increases progressively from its bottom end to its upper end; and

(d) at least one side wall of each section is formed at spaced points thereon with depressions of progressively increased depth and of elongated shape, and which depressions are inclined to the longitudinal axis of the sections such that the side walls contact at regions spaced from their edges to form obstructions which cause liquid adapted to flow through the sections to follow an alternating from front to back tortuous path.

4. A heat exchanger as claimed in claim 3, wherein the side walls are secured together at the region of contact by welding.

5. A heat exchanger as claimed in claim 3, wherein the sections are each connected with the top and bottom headers adjacent the respective ends of one longitudinal edge of the section.

References Cited UNITED STATES PATENTS 1,550,154 8/1925 Faccioli 33658 X 2,444,825 7/1948 Highley 165-146 708,712 9/1902 Hill 165147 1,838,722 12/1931 Watson 16517 8 X 2,935,664 5/1960 Scharli 165l34 X FOREIGN PATENTS 573,208 3/ 1924 France. 546,983 9/ 1922 France.

ALBERT W. DAVIS, JR., Primary Examiner U.S. Cl. X.R. 

